The present invention relates to a high strength gear, particularly of the kind that can be successfully used in a drive train of a high output engine and can attain an improved wear resistance and an elongated life. The present invention further relates to a method of producing such a high strength gear.
Heretofore, carburizing steels or carbonitriding steels are generally used for gears for automotive transmissions. With the tendency that the output of the engine has been becoming higher in these years, damages such as pitting, spalling and wear, to be caused in a tooth surface of a gear has given rise to a problem.
As a countermeasure to this problem, it is considered to coat the tooth surface of the gear with a hard coating. An example of a hard coating formed on a sliding member is disclosed in Japanese Patent Provisional Publication No. 5-78821. Namely, by the publication, it has been proposed a piston ring that is improved in the wear resistance by being coated with a coating formed of a mixed texture of at least one metal selected from the group consisting of Ni, Co and Mo and carbide or nitride of at least one metal selected from the group consisting of Cr, Ti and W.
Further, it is proposed by Japanese Patent Publication No. 10-167348 to coat a gear with a titanium nitride coating for the purpose of improving the pitting resistance.